Enhanced utility disturbance monitor

Abstract

A method for detecting a voltage disturbance on an electrical line coupled to a utility that includes calculating a sliding window actual root mean squared (RMS) voltage for each three-phase power signal, calculating a sliding window filtered RMS average voltage for each actual RMS voltage to identify normal changes in the voltage of the power signals from a nominal voltage, and obtaining a difference between the actual RMS voltage and the RMS average voltage for each of the power signals. The method determines whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is greater than a first predetermined percentage, or whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is less than a second predetermined percentage, and if so, disconnects a load from the utility.

What is claimed is: 
     
       1. A method for detecting a voltage disturbance on an electrical line coupled to a utility, where the utility provides three-phase electrical AC power signals on the line to an electrical system, said method comprising:
 reading instantaneous voltage measurements of each of the three-phase power signals on the electrical line at a predetermined sample rate; 
 calculating a sliding window actual root mean squared (RMS) voltage of each three-phase power signal at the sample rate over a first predetermined sample period using the instantaneous voltage measurements; 
 calculating a sliding window filtered RMS average voltage of each three-phase power signal at the sample rate over a second predetermined sample period to identify voltage changes of the three-phase power signals from a nominal voltage; 
 determining whether any of the actual RMS voltages is greater than a first predetermined percentage of the nominal voltage at the sample rate; 
 determining whether any of the actual RMS voltages is less than a second predetermined percentage of the nominal voltage at the sample rate; 
 obtaining a difference between the actual RMS voltage and the RMS average voltage for each of the three-phase power signals at the sample rate; 
 determining whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase power signals is greater than a third predetermined percentage at the sample rate; 
 determining whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is less than a fourth predetermined percentage at the sample rate; and 
 detecting the voltage disturbance if any of the actual RMS voltages is greater than the first predetermined percentage or any of the actual RMS voltages is less than the second predetermined percentage or the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase power signals is greater than the third predetermined percentage or the difference between the actual RMS voltage and the RMS average voltage of any of the three-phase power signals is less than the fourth predetermined percentage. 
 
     
     
       2. The method according to  claim 1  wherein the predetermined sample rate is 4800 samples per second. 
     
     
       3. The method according to  claim 1  wherein the first predetermined sample period is a one-half AC cycle of the three-phase power signals. 
     
     
       4. The method according to  claim 1  wherein the second predetermined sample period is a full AC cycle of the three-phase power signals. 
     
     
       5. The method according to  claim 1  wherein the first predetermined percentage is 110% of the nominal voltage, the second predetermined percentage is 90% of the nominal voltage, the third predetermined percentage is 10% and the fourth predetermined percentage is −10%. 
     
     
       6. The method according to  claim 1  wherein calculating a sliding window filtered RMS average voltage includes calculating the RMS average voltages as a percentage of an actual voltage of the three-phase power signals so that the calculated RMS average voltages will be equal to the actual voltage after a predetermined time constant. 
     
     
       7. The method according to  claim 6  wherein the predetermined time constant is about five minutes. 
     
     
       8. The method according to  claim 1  wherein the electrical system is a critical load or a micro-grid. 
     
     
       9. The method according to  claim 1  further comprising disconnecting the electrical system from the utility if the voltage disturbance is detected. 
     
     
       10. A method for detecting a voltage disturbance on an electrical line coupled to a utility, where the utility provides an AC power signal on the line to an electrical system, said method comprising:
 reading an instantaneous voltage measurement of the power signal on the electrical line at a predetermined sample rate; 
 calculating a sliding window actual root mean squared (RMS) voltage of the power signal at the sample rate over a first predetermined sample period using the instantaneous voltage measurements; 
 calculating a sliding window filtered RMS average voltage of the power signal at the sample rate over a second predetermined sample period to identify voltage changes of the power signal from a nominal voltage; 
 obtaining a difference between the actual RMS voltage and the RMS average voltage for the power signal at the sample rate; 
 determining whether the difference between the actual RMS voltage and the RMS average voltage for the power signal is greater than a first predetermined percentage at the sample rate; 
 determining whether the difference between the actual RMS voltage and the RMS average voltage for the power signal is less than a second predetermined percentage at the sample rate; and 
 detecting the voltage disturbance if either the difference between the actual RMS voltage and the RMS average voltage for the power signal is greater than the first predetermined percentage or the difference between the actual RMS voltage and the RMS average voltage of the power signal is less than the second predetermined percentage. 
 
     
     
       11. The method according to  claim 10  wherein the predetermined sample rate is 4800 samples per second. 
     
     
       12. The method according to  claim 10  wherein the first predetermined sample period is a one-half AC cycle of the power signal. 
     
     
       13. The method according to  claim 10  wherein the second predetermined sample period is a full AC cycle of the power signal. 
     
     
       14. The method according to  claim 10  wherein the first predetermined percentage is 10% and the second predetermined percentage is −10%. 
     
     
       15. The method according to  claim 10  wherein calculating a sliding window filtered RMS average voltage includes calculating the RMS average voltages as a percentage of an actual voltage of the power signal so that the calculated RMS average voltages will be equal to the actual voltage after a predetermined time constant. 
     
     
       16. The method according to  claim 15  wherein the predetermined time constant is about five minutes. 
     
     
       17. The method according to  claim 10  wherein the electrical system is a critical load or a micro-grid. 
     
     
       18. The method according to  claim 10  further comprising disconnecting the electrical system from the utility if the voltage disturbance is detected. 
     
     
       19. The method according to  claim 10  wherein the power signal is a three-phase power signal. 
     
     
       20. A method for detecting a voltage disturbance on an electrical line coupled to a utility, where the utility provides three-phase electrical AC power signals on the line to an electrical system, said method comprising:
 reading instantaneous voltage measurements of each of the three-phase power signals on the electrical line at a predetermined sample rate of 4800 samples per second; 
 calculating a sliding window actual root mean squared (RMS) voltage of each three-phase power signal at the sample rate over a first predetermined sample period of a one-half AC cycle of the power signal using the instantaneous voltage measurements; 
 calculating a sliding window filtered RMS average voltage of each three-phase power signal at the sample rate over a second predetermined sample period of a full AC cycle of the power signal to identify voltage changes of the three-phase power signals from a nominal voltage; 
 determining whether any of the actual RMS voltages is greater than a first predetermined percentage of 110% of the nominal voltage at the sample rate; 
 determining whether any of the actual RMS voltages is less than a second predetermined percentage of 90% of the nominal voltage at the sample rate; 
 obtaining a difference between the actual RMS voltage and the RMS average voltage for each of the three-phase power signals at the sample rate; 
 determining whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase signals is greater than a third predetermined percentage of 10% at the sample rate; 
 determining whether the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase power signals is less than a fourth predetermined percentage of −10% at the sample rate; 
 detecting the voltage disturbance if any of the actual RMS voltages is greater than the first predetermined percentage or any of the actual RMS voltages is less than the second predetermined percentage or the difference between the actual RMS voltage and the RMS average voltage for any of the three-phase power signals is greater than the third predetermined percentage or the difference between the actual RMS voltage and the RMS average voltage of any of the three-phase power signals is less than the fourth predetermined percentage; and 
 disconnecting the electrical system from the utility if the voltage disturbance is detected.